1. Field of the Invention
The present invention relates to the destruction, or consumption, of hypochlorites or ClO.sup.- ions present in a perchlorate solution of an alkali metal, such as the solution of sodium perchlorate resulting from the electrolysis of an aqueous solution of the chlorate of said alkali metal, for example a solution of sodium chlorate, prior to the crystallization of the perchlorate values therefrom.
2. Description of the Prior Art
Except for allowing the perchlorate solution to remain in a so-called evolution reactor upon its withdrawal from the electrolysis cell for a period of time that is incompatible with the requirements of industrial production, it is known to this art that significant amounts of hypochlorite remain in such solution after evolution, to cause significant corrosion of the crystallizer, which typically is made of carbon or stainless steel.
It is also known to introduce additives into the perchlorate solutions, such as, for example, urea. But urea may form chloramines, which themselves are corrosive and which present the risk of explosion.
Thus, serious need continues to exist in this art for means other than mere passage of time or the above additives for destroying as completely as possible the hypochlorite values contained in a perchlorate solution prior to the crystallization of the perchlorate.
Although it is known that hydrogen peroxide reacts with ClO.sup.- ions, no process has to date been described for the destruction of such ions by means of H.sub.2 O.sub.2 introduced into an alkali metal perchlorate solution emanating from the electrolysis of a chlorate solution of said alkali metal, in particular if hexavalent chromium is also present.
Hexavalent chromium, which, as is known to the art, makes it possible to minimize the phenomenon of cathodic reduction, should be retained in the loop to the extent possible in the electrolytic recirculation system for the production of perchlorate, both for economic and technical reasons. The hexavalent chromium is employed most typically in the form of a bichromate thereof, such as sodium bichromate.
In light of the great sensitivity of hydrogen peroxide, an ineffective destruction of the hypochlorites and/or the disappearance of the hexavalent chromium would be expected results, as in the case of, for example, the destruction of hypochlorites by sulfides soluble in water, as described in FR 2,168,530.